Starting with version 9, Java does not permit access to internal JARs such as lib/ant-javax.jar, lib/dt.jar and others listed in the lib directory shown here:
The key thing to note here is that if you have Java applications that are dependent on one of these tools residing in the lib folder, you will need to modify your code accordingly.
It is recommended that you test your IDE once you start using Java 10 and 11 to ensure the IDE is updated and officially supports the latest version of Java. If you use more than one IDE for Java development, test each one to avoid surprises.